This invention relates to ignition coils and more particularly to ignition coils arranged in a cassette format.
The ignition of the fuel-air mixture in the combustion chamber of an internal combustion engine is done by a sparkplug in which a high voltage spark generated by a coil causes a discharge across a firing or spark gap of the sparkplug. The ignition coil itself is charged with energy and discharges at a predetermined time, which may be controlled by a computer. The coil discharge causes the spark to flash over at the spark gap and the spark gap ignites the combustion mixture within the combustion chamber of the internal combustion engine. Whereas a single coil has traditionally been used to control the discharge of a plurality of spark plugs, more recently systems have been employed in which a separate coil is provided for each sparkplug. A typical system includes a coil for each cylinder or spark plug, a coil driver for each coil, one or more crankshaft position sensors, and a camshaft position sensor. The coils can be mounted as inductive coil per cylinder systems or integrated into cassettes.
Highest efficiency and lowest electromagnetic radiation is attained by integrating the coils into cassettes specifically designed for the engine and located just above the spark plugs. The ignition cassette is typically installed in the cylinder head valve cover and each ignition coil is connected directly to its corresponding sparkplug by a secondary boot and spring so there is no need for secondary leads. Because the secondary leads are eliminated and all of the ignition components of the system are contained in a single cassette for each cylinder bank, installation of the ignition system onto the engine is simplified.
Whereas the ignition cassette arrangement has proven to be generally satisfactory, the assembly of the cassette is rather complicated and somewhat labor intensive. There is accordingly a need to simplify the construction and assembly of the ignition cassette system.
This invention is directed to ignition coil cassette assemblies.
More specifically, this invention is directed to an ignition coil cassette assembly which may be manufactured at lower cost and which provides minimal thermal resistance.
The methodology aspect of the invention concerns a method of assembly an ignition coil cassette assembly for use with an internal combustion engine having a plurality of cylinder assemblies each including a spark plug. The cassette assembly includes a plurality of ignition coils for respective electrical coupling to the respective spark plugs to deliver high voltage charges to the spark plugs in accordance with a predetermined firing order, a cassette body structure interconnecting and mounting the ignition coils in spaced downstanding relation with respect to the body, and a printed circuit board for delivering power to the coils and including electronic components mounted on the board.
According to the invention methodology, a plurality of upwardly opening pockets are provided in the cassette body; the electric components are positioned in the pockets; the ignition coils are positioned in the cassette body; the printed circuit board is positioned in overlying relation to the electronic components and upper ends of the ignition coils; and upstanding pins on the electronic components are soldered to the printed circuit board while simultaneously soldering upstanding pins on the upper ends of the ignition coils to the printed circuit board. This methodology allows the electronic components to be soldered to the printed circuit board in the same wave soldering operation utilized to solder the coils to the printed circuit board.
According to a further feature of the invention methodology, the method includes the further step of encapsulating the printed circuit board in an epoxy material following soldering of the electronic component and the ignition coil pins to the printed circuit board. This methodology facilitates the insulative packaging of the cassette.
According to a further feature of the invention methodology, an upper face of the cassette body has an upwardly opening bathtub configuration overlying the upper ends of the ignition coils, and the printed circuit board is positioned in the bathtub configuration in overlying relation to the ignition coils. This methodology provides a convenient means of positively positioning and packaging the circuit board to the cassette body.
According to a further feature of the invention methodology, the epoxy material is poured into the bathtub configuration following positioning of the printed circuit board in the bathtub configuration and soldering of the electronic component pins and the ignition coil pins to the printed circuit board. With this methodology, the bathtub configuration of the cassette body serves to contain and define the extent of the epoxy material.
According to a further feature of the invention methodology, the electronic components comprise drivers for the respective coils; each driver includes a heatsink element; and the pockets are configured to tightly receive the drivers and included heatsink elements. This methodology facilitates the secure placement of the drivers in the cassette body and facilitates heat dissipation.
According to a further feature of the invention methodology, each pocket, in cross-section, includes an upper main body upwardly opening portion sized to tightly receive the driver and heatsink element and a lower portion sized to tightly receive a tab portion of the respective heatsink element extending below the associated driver. This methodology positively locates the driver in the cassette body and minimizes the resistance between the driver and ambient whereby to facilitate heat dissipation.
According to a further feature of the invention methodology, the upper main body portion of each pocket includes crush ribs which operate in response to insertion of a driver and associated heatsink element into the pocket to push the heatsink element against an opposite wall of the pocket. This methodology insures a tight fit between the heatsink element and the confronting wall of the pocket whereby to further minimize thermal resistance between the driver and ambient.
According to a further feature of the invention methodology, the pockets are defined by thin walls of the cassette body whereby to further facilitate heat dissipation.
According to an apparatus aspect of the invention, an ignition coil assembly is provided for use with an internal combustion engine having a plurality of cylinder assemblies each including a spark plug, the cassette assembly including a plurality of ignition coils for respective electrical coupling to the respective power plugs, whereby to deliver high voltage charges to the spark plugs in accordance with a predetermined firing order, a cassette body structure interconnecting and mounting the ignition coils in spaced downstanding relation with respect to the body, and a printed circuit board for delivering power to the coils and including electronic components mounted on the board.
According to the invention apparatus, a plurality of upwardly opening pockets are provided in the cassette body; the electronic components are positioned in the pockets and include upstanding pins; and the printed circuit board is positioned in overlying relation to the electronic components and upper ends of the ignition coils with the upstanding pins on the electronic components and upstanding pins on the ignition coils extending upwardly through openings in the printed circuit board for soldering connection to the printed circuit board. This construction facilitates the attachment of the electronic components to the printed circuit board and specifically allows the electronic components to be soldered to the printed circuit board in the same wave soldering operation that solders the coils to the printed circuit board.
According to a further feature of the invention apparatus, the printed circuit board and the electronic components are encapsulated in an epoxy material. This arrangement provides a convenient and effective insulator packaging for the cassette assembly.
According to a further feature of the invention apparatus, an upper face of the cassette body has an upwardly opening bathtub configuration overlying the upper ends of the ignition coils and the printed circuit board is positioned in the bathtub configuration in overlying relation to the ignition coils. This arrangement provides a convenient packaging for the printed circuit board with respect to the cassette body.
According to a further feature of the invention apparatus, the epoxy material is contained in the bathtub configuration in surrounding relation to the printed circuit board. This arrangement facilitates the containment and the definition of the epoxy material.
According to a further feature of the invention apparatus, each ignition coil comprises a pencil coil having a core, secondary winding, and primary winding arranged in concentric relation. The use of pencil coils facilitates the use of the cassette configuration.
According to a further feature of the invention apparatus, the electronic components comprise drivers for the respective coils, each driver includes a heatsink element, and the pockets are configured to tightly receive the drivers and included heatsink elements. This specific pocket construction facilitates the mounting of the drivers in the cassette body.
According to a further feature of the invention apparatus, each pocket, in cross-section, includes an upper main body upwardly opening portion sized to receive the driver and heatsink element and a lower portion sized to tightly receive a tab portion of the respective heatsink element extending below the associated driver. This specific pocket configuration facilitates the mounting of the drivers in the cassette body and optimizes the heat dissipation from the drivers.
According to a further feature of the invention apparatus, the upper main body portion of each pocket includes crush ribs which operate in response to insertion of the driver and associated heatsink element into the pocket to push the heatsink element against an opposite wall of the pocket. This arrangement further facilitates the heat dissipation from the drivers.
According to a further feature of the invention apparatus, the pockets are defined by thin walls of the cassette body. This arrangement further facilitates heat dissipation.
Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.